In a mobile communications network, a wireless relay technology is mainly used for hotspot coverage, cell expansion, emergency, a in-vehicle scenario, and cell coverage enhancement. As shown in FIG. 1, in the mobile communications network, a wireless relay device 101 may be classified into two parts. One part is configured to communicate with a macro base station, where the macro base station is an evolved NodeB (eNB) 102, and this part is referred to as R-UE104. The other part is configured to communicate with user equipment (UE) 103, and the other part is referred to as an R-eNB105. An interface between the eNB and the relay device is a backhaul link, and an interface between the relay device and the UE is an access link. In a practical application, frequencies are configured for the backhaul link and the access link according to a requirement. However, when adjacent frequency bands are configured for the backhaul link and the access link, adjacent-channel interference may be caused in relay transmitting and receiving.
As shown in FIG. 2, 60 MHz spectrum resources are available, and 20 MHz is used as one frequency band to divide the available spectrum resources into three frequency bands, which are successively f1, f2, and f3. As shown in FIG. 1, a backhaul link uses a frequency band fb, and a access link uses a frequency band fa. When the frequency band fb is the f1, and the frequency band fa is the f2, the backhaul link and the access link use adjacent frequency bands, and adjacent-channel interference may be caused between an R-UE antenna and an R-eNB antenna. For example, when the R-UE104 receives downlink data transmitted by the eNB102, the R-UE104 is interfered by a signal transmitted by the R-eNB105 to the UE103. As a result, the R-UE104 is unable to normally receive a signal transmitted by the eNB102.
Adjacent-channel interference mainly includes two types: spurious interference and blocking interference. The spurious interference refers to additive interference generated by an interference source in an operating frequency band of an interfered receiver, including out-of-band power leakage, a transmit intermodulation product, transmission background noise, and the like of the interference source, and the additive interference may deteriorate a signal-to-noise ratio of the interfered receiver. The blocking interference refers to a strong interference signal out of the operating frequency band of the interfered receiver, and the strong interference signal may lead to receiver saturation, cause a gain decrease, generate interference in an intermediate frequency after being mixed with a local-frequency signal, and directly cause interference because of limited out-of-band suppression. Generally, the receiver works in a linear range. When a strong interference signal enters the receiver, the receiver is to work in a nonlinear state, and the receiver saturation is even caused.
In order to avoid interference between transmit and receive antennas of the R-UE and the R-eNB, definite isolation is required between a receiver Rx and a transmitter Tx. For example, when a guard interval between the frequency band fa and the frequency band fb is 0 MHz, the isolation between the Rx and the Tx is required to be 111 dB. When the guard interval between the frequency band fa and the frequency band fb is 5 MHz, the isolation between the Rx and the Tx is required to be 103 dB; in this case, if the frequency band fa occupies the frequency band f1 in FIG. 2, the guard interval occupies 5 MHz bandwidth of the frequency band f2, and the frequency band fb can only occupy part of bandwidth of the frequency band f2. When the guard interval between the frequency band fa and the frequency band fb is 20 MHz, the isolation between the Rx and the Tx is required to be 84 dB; in this case, the frequency band fa may occupy the frequency band f1 in FIG. 2, the guard interval occupies the frequency band f2, and the frequency band fb occupies the frequency band f3.
To meet a requirement for isolation between the transmit and receive antennas, two technical solutions are mainly used currently. For details, refer to Table 1.
TABLE 1Guard intervalbetween thebackhaul linkand the accesslink0 MHz5 MHz20 MHzSolution 1:The Rx and theThe Rx and theThe Rx and the TxphysicalTx are placedTx are placedare placed backisolationback to back; aback to back; ato back; arequirementrequirementrequirement forfor a distancefor a distancea distancebetween thebetween thebetween thetransmit andtransmit andtransmit andreceivereceivereceive antennasantennas is:antennas is:is:1.5 m1.4 m0.8 m horizontalhorizontalhorizontalspacing; andspacing; andspacing; and0.8 m vertical1 m vertical1 m verticalspacing.spacing.spacing.Solution 2:The filter isThe filter isThe filter isphysicaladded.added.added.isolation withThe Rx and theThe Rx and theThe Rx and the Txa filter addedTx are placedTx are placedare placed backback to back; aback to back; ato back; arequirementrequirementrequirement forfor a distancefor a distancea distancebetween thebetween thebetween thetransmit andtransmit andtransmit andreceivereceivereceive antennasantennas is:antennas is:is:1.4 m0.5 m0.5 m horizontalhorizontalhorizontalspacing; andspacing; andspacing; and0.5 m vertical1 m vertical0.5 m verticalspacing.spacing.spacing.
In the solution 1, a physical isolation method is used to adjust placing positions of the Rx and the Tx to keep a large enough distance between the Rx and the Tx, so as to reduce the interference between the transmit and receive antennas. However, this method requires a large distance between the transmit and receive antennas on the relay device, which brings difficulty to installation of the relay device, and is unfavorable to product integration of the relay device. In the solution 2, the filter is added between the Rx and the Tx based on the physical isolation, so as to further reduce the interference between the transmit and receive antennas. Compared with the solution 1, the solution 2 relatively lowers a requirement for spacing between the Rx and the Tx, but still has a relatively high requirement for the spacing. In addition, because the filter needs to be added, a volume of the relay device is enlarged, and a cost of the relay device is increased. Moreover, when the volume of the device is required to be less than or equal to 0.5 m3, the backhaul link and the access link need to be isolated by at least 5 MHz, and consequently adjacent frequency bands cannot be configured for the backhaul link and the access link. Therefore, configuration flexibility of the backhaul link and the access link is limited.